Gas mixer for blast furnace stoves



Nov. 16, 1965 G. R. CURTIS ETAL GAS MIXER FOR BLAST FURNACE STOVES FiledApril 5, 1963 INVENTOR. GERALD R. CURTIS AND NEAL T KURFISS ATTORNEYSUnited States Patent 3,217,781 GAS MIXER FOR BLAST FURNACE STOVES GeraldR. Curtis and Neal T. Kurfiss, Middletown, Ohio, assignors to ArmcoSteel Corporation, Middletown, Ohio, a corporation of Ohio Filed Apr. 5,1963, Ser. No. 270,850 8 Claims. (Cl. 158-109) This invention relates toburners for blast furnace stoves, and more particularly to a device forthoroughly mixing a gaseous fuel and air therein.

A modern blast furnace installation will include two or more stoves,each of which is a large structure substantially filled with refractorycheckerwork. At any given time, one of these stoves is on the line; thatis, cold air is passed through the checkerwork, and fed into the blastfurnace. At the same time, the other stoves are on gas. This means thatfuel gas and air are burned in a combustion chamber, and the products ofcombustion are directed through the checkerwork to heat up the stove. Atsuitable time intervals, the various stoves are alternated so that thesupply of air to the blast furnace is maintained at a high temperature.

Burners for such stoves generally utilize blast furnace gas as fuel,primarily because of its ready availability. However, such gas ischaracterized by a relatively low calorific value. This of course meansthat a large volume of gas must be burned; as a result, the burners aregenerally operated at a rather high speed. A common problem in such anoperation is what may be called backfiring. This is due in very largepart to an insufficient mixing of the gaseous fuel and combustion air,so that the gases do not ignite at the mouth of the burner. Hence thereis a delayed ignition, occurring probably when the gas reaches thebegining of the checkerwork, with a resulting explosion and flash back.At that time, the flame will go out until the gas again returns to thebeginning of the checkerwork.

Accordingly, a primary object of this invention'is to provide a mixingdevice which will improve the mixing of gas and air, and preventpulsating explosions at high burning rates.

Another object of this invention is the provision of such a device whichwill accomplish the thorough mixing Without using any moving parts orrequiring additional energy.

While it is very desirable to have ignition occur at the mouth of theburner, it will immediately be apparent that combustion cannot bepermitted within the mixer itself. For this reason, prior art devicesmaintain the gas and air in separate conduits until they enter thecombustion chamber, and then attempt to induce sufficient turbulence toaccomplish the necessary mixing at that point.

It is therefore still another object of the present invention to providea device in which mixing is accomplished within the mixer, but in whichcombustion is prevented until the gases reach the entrance to thecombustion chamber.

Still a further object of this invention is the provision of a mixerconfiguration which, while very eificient in producing violentturbulence, is very easy to fabricate.

Other objects of this invention will become apparent as thisspecification proceeds. Reference will be made from time to time to theaccompanying drawings forming a part hereof, and in which:

FIGURE 1 is a vertical cross-sectional view through the device of thisinvention, and

FIGURE 2 is a perspective view showing a portion of the deviceillustrated in FIGURE 1.

Broadly considered, the mixer of this invention includes two concentricconduits, with a high pressure gas (either fuel or air) flowing throughthe inside conduit,

and a lower .pressure gas (again either fuel or air) carried by theoutside conduit. This invention also includes a stationary whirler whichutilizes the pressure differential between the two gas streams to supplythe energy to accomplish the complete admixture of the gases.

Referring now to FIGURE 1, the inside conduit has been designated at 10,and the outside conduit at 11. In the embodiment shown, the outsideconduit includes a portion 11a which is suitably joined to the portion11 with an air-tight seal as at 12. This two-piece construction ispreferred'in order that the portion 11a may be removed and a door (notshown) may be placed over the entrance to the combustion chamber whenthe stove is on the line. In any event, it will certainly be understoodthat the out-' side conduit can be made in one piece, in which asuitable valve, preferably water cooled, must be provided to close theopening into the combustion chamber.

According to conventional practice, a blast furnace is operated atsuper-atmospheric pressure; hence the top gas coming from the furnace isunder pressure when it reaches the burner. In the embodimentillustrated, the fuel gas under relatively high pressure is shown byfull line arrows as passing through the inside conduit 10; but it willbe understood that if desired the gaseous fuel could be passed throughthe outside conduit, and the air for combustion through the insideconduit. Further in the embodiment shown, air for combustion will be fandriven through the outer conduit 11, and its passage is indicated by thedotted arrows. A fan has not been shown in the drawing, but it will beunderstood that it is conventional in construction, and as such, formsno part of this invention. It is only necessary to provide a pressurizedsupply of gas through the inside conduit 10, and a supply of gas undersomewhat lower pressure through the outer conduit 11.

The mixing device itself includes two principal parts. The first ofthese is a frustum shaped deflector ring indicated at 13. As shown inthe drawings, the ring 13 is mounted within the inside conduit 10, andserves two important functions. First, it acts to deflect a portion ofthe high pressure gas stream outwardly, and secondly, it defines anorifice which serves to increase the velocity of the high pressurestream. This of course ultimately results in better mixing.

The stationary whirler can best be described by referring at this timeto FIGURE 2. As seen therein, it includes four mixing vanes indicated at14, although the number of vanes is not critical. Each of these vanes isformed to provide a curved surface, but it will be noted that the curvedsurface is bounded by three straight lines. That is, each vane has astraight base 15, a straight leading edge 16, and a straight trailingedge 17. The opposite side edge 18 of each vane is curved, but it willbe noted that the shortest distance from every point along the oppositeside edge to the base is constant. This particular construction of themixing vane has two primary advantages. In the first place, it is veryefiicient in imparting a swirling or rotary motion to the high pressurestream of gas and directing a portion of it outwardly into the lowpressure stream of gas, and in the second place, it is very easy tofabricate.

As clearly shown in FIGURE 2, the four vanes are joined together attheir bases 15, and spaced approximately of rotation apart. The spacedapart circular rings 19 and 20 are secured to the opposite side edges ofall four of the vanes. Each of these rings is provided with a number ofoutwardly projecting flanges 21, by means of which the stationarywhirler may be secured within the outside conduit 11a. It will beapparent that at high operating rates, the whirler develops a great dealof torque, and certain reinforcements in the mounting arrangement aredesirable. For example, straps 22 (FIG- URE 2) may be mountedtangentially between the bases Patented Nov. 16,. 1965 9 of the flanges21 and the outer conduit 11a. These straps Simply act as tension membersto prevent rotation.

At this time, it should be noted that the inside conduit terminates ashort distance in back of the stationary whirler. It will therefore beapparent that beyond the end of the inside conduit, yet still within theoutside conduit 11a, there can be a complete admixture of the gaseousfuel and the air for combustion.

Optimum performance requires that the gases be ignited at the mouth ofthe burner as soon as the mixture enters the combustion chamber at apoint indicated in FIG. 1 generally at 23. The combination of thefrustum deflector ring 13 and the mixing vanes 14 produce a violentturbulence which will insure complete mixing of the gases prior toleaving the mixer, and insures ignition at the mouth of the burner 23.

To prevent the flame from backing up into the burner, the gas mixture,while in the mixer itself, must be maintained at a velocity which isgreater than the flame propagation rate. By operating the mixture at ahigh velocity, it is not necessary to keep the gas and air separateduntil they enter the combustion chamber. With this invention, mixing canbe accomplished within the mixing device itself, and combustion will notoccur until the velocity of the mixture drops at the entrance to thecombustion chamber.

Numerous modifications in this invention will readily present themselvesto the skilled worker in the art. Hence, although the invention has beendescribed in terms of an exemplary embodiment, no limitation is intendedexcept insofar as set forth in the following claims.

What is claimed as new and what it is desired to secure by LettersPatent is:

1. A gas mixer for blast furnace stoves comprising a first conduit forthe passage of gas under pressure, a second conduit surrounding saidfirst conduit to form an annular chamber for the passage of gas underpressure, said second conduit extending beyond the end of said firstconduit, means including a ring shaped deflector concentrically disposedwithin said first conduit at the outer end thereof to direct a portionof said gas under pressure outwardly, and a stationary whirler meansmounted within said second conduit and beyond the end of said firstconduit, said stationary whirler means being aligned coaxially with saidfirst conduit and including a plurality of mixing vanes disposed toimpart rotary movement to said gas leaving said first conduit, and toeffect the mixing of said gases leaving said first and second conduitsrespectively.

2. The gas mixer claimed in claim ll, wherein said mixing vanes of saidstationary whirler means each comprise a curved surface having astraight base, a straight leading edge, a straight trailing edge, and acurved opposite side edge.

3. The gas mixer claimed in claim 1, wherein said ring shaped deflectorcomprises a frustum ring, the larger end of said ring being mountedwithin and spaced from the inner wall of said first conduit.

4. The gas mixer claimed in claim 2, wherein said stationary whirlermeans includes four mixing vanes, said vanes being joined together alongsaid straight bases and spaced substantially apart.

5. The gas mixer claimed in claim 2, wherein the shortest distancebetween every point along said curved opposite side edge and saidstraight base of each of said vanes is constant.

6. A gas mixer for blast furnace stoves comprising a first conduit forthe passage of gas under high pressure, a second conduit surroundingsaid first conduit to form an annular chamber for the passage of gasunder low pressure, said second conduit having an end portion thereofextending beyond the end of said first conduit, and a stationary whirlermeans mounted in said second conduit beyond the end of said firstconduit and coaxial therewith, said whirler means having a plurality ofmixing vanes disposed to impart rotary movement to said high pressuregas and to divert a portion of said high pressure gas outwardly foradmixture with the low pressure gas flowing through the said extendingend portion of said second conduit, each said vanes comprising a curvedsurface having a straight base, a straight leading edge, a straighttrailing edge, and a curved opposite side edge.

7. The gas mixer claimed in claim 6, wherein the shortest distancebetween every point along said curved opposite side edge and saidstraight base of each of said vanes is constant.

8. The gas mixer claimed in claim 1 wherein the outermost edges of saidvanes are secured to a ring the diameter of which is approximately equalto the diameter of said first conduit.

References Cited by the Examiner UNITED STATES PATENTS 850,996 4/1907Cooley 158118 1,071,053 8/1913 Hunter 158l09 1,360,981 11/1920 Witt158118 1,885,067 10/1932 Woodeson -104 1,893,533 1/1933 Barber 158l18JAMES W. WESTHAVER, Primary Examiner.

1. A GAS MIXER FOR BLAST FURNACE STOVES COMPRISING A FIRST CONDUIT FORTHE PASSAGE OF GAS UNDER PRESSURE, A SECOND CONDUIT SURROUNDING SAIDFIRST CONDUIT TO FORM AN ANNULAR CHAMBER FOR THE PASSAGE OF GAS UNDERPRESSURE, SAID SECOND CONDUIT EXTENDING BEYOND THE END OF SAID FIRSTCONDUIT, MEANS INCLUDING A RING S HAPED DEFLECTOR CONCENTRICALLYDISPOSED WITHIN SAID FIRST CONDUIT AT THE OUTER END THEREOF TO DIRECT APORTION OF SAID GAS UNDER PRESSURE OUTWARDLY, AND A STATIONARY WHIRLERMEANS MOUNTED WITHIN SAID SECOND CONDUIT AND BEYOND THE END OF SAIDFIRST CONDUIT, SAID STATIONARY WHIRLER MEANS BEING ALIGNED COAXIALLYWITH SAID FIRST CONDUIT AND INCLUDING A PLURALITY OF MIXING VANESDISPOSED TO IMPART ROTARY MOVEMENT TO SAID GAS LEAVING SAID FIRSTCONDUIT, AWND TO EFFECT THE MIXING OF SAID GASES LEAVING SAID FIRST ANDSECOND CONDUITS RESPECTIVELY.